Interpretive Summary: In the gas chromatographic (GC) analysis of certain types of pesticides, active sites in the inlet and column cause losses and tailing of the pesticide peak. However, in the presence of complicated food extracts, the effect is reduced because the active sites are filled up by the matrix components. Thus, to avoid quantitation inaccuracies for susceptible pesticides, calibration standards are commonly prepared in matrix blanks. However, this is inconvenient because extra blanks and work are needed. Furthermore, the current policies of the Food and Drug Administration and Environmental Protection Agency do not permit the use of calibration standards in matrix for regulatory enforcement actions. Thus, a new approach was devised in which "analyte protectants" were used to mask the active sites in the GC system. This paper describes the optimization to the analyte protectant concept by using a mixture of 3 different protecting agents. The benefits of using analyte protectants vs. alternative procedures for overcoming matrix-induced effects in quantitation include: a) simpler procedure; b) easier integration of peaks; c) lower detection limits; d) more accurate results; e) less maintenance of the GC system; and e) lower cost.

Technical Abstract:
Analyte protectants were previously defined as compounds that strongly interact with active sites in the gas chromatographic (GC) system, thus decreasing degradation and/or adsorption of co-injected analytes. In this study, we evaluated various combinations of promising analyte protectants for the volatility range of GC-amenable pesticides using GC-quadrupole mass spectrometry (MS) and 1 'L hot splitless injection for sample introduction. A mixture of ethylglycerol, gulonolactone, and sorbitol (at 10, 1, and 1 mg/mL, respectively, in the injected samples) was found to be the most effective in minimizing losses of susceptible analytes and significantly improving their peak shapes (due to reduction of peak tailing). When added to final sample extracts and matrix-free calibration standards alike, these analyte protectants induced a similar response enhancement in both instances, resulting in effective equalization of the matrix-induced response enhancement effect even after a large number of fruit and vegetable extract injections. As compared to matrix-matched standardization, the analyte protectant approach offers a more convenient solution to the problems associated with calibration in routine GC-MS analysis of pesticide residues and possibly other susceptible analyte types in diverse samples. Moreover, the use of analyte protectants also substantially reduced another adverse matrix- related effect caused by gradual build-up of non-volatile matrix components in the GC system, thus improving ruggedness and, consequently, reducing need for frequent maintenance.